The present invention generally relates to communication control units, and more particularly to a communication control unit which can select a control mode of data communication.
Recently, there are increasing demands for data communication due to developments of an integrated services digital network (ISDN) and the like.
In data communications, the call control is carried out by a line interface part, and the control of a data terminal is carried out by a data communication part. The line interface part and the data communication part are both controlled by a central processing unit (CPU).
By the progress in large scale integrated circuit (LSI) technology and application specific integrated circuit (ASIC) technology which is used to form a plurality of circuits on a single semiconductor chip, there is a proposed communication controller which integrally comprises various circuits such as the line interface part and the data communication part with the CPU provided as a core.
On the other hand, there are various types of data communication, including simple and complex data communication. For example, the control of the line interface part and the control of the data communication part may be carried out by independent CPUs or by a single CPU. For this reason, when designing the communication control unit in which the various circuits such as the line interface part and the data communication part are integrated using the CPU as the core, the architecture must be flexible so that the communication control unit can cope with various data terminals such as a data terminal which uses a complicated procedure and has a large number of functions, a data terminal which uses a simple procedure and has a relatively small number of functions and a data terminal having a plurality of ports. In this specification, the data terminal which uses the complicated procedure and has the relatively large number of functions will be referred to as a complex data terminal, and the data terminal which uses the simple procedure and has the relatively small number of functions will be referred to as a simple data terminal.
FIG. 1 shows an example of a conventional communication control unit. The communication control unit includes CPUs 101 and 102, a line interface part 103 which makes a call control, a data communication part 104 for controlling a data terminal, and an interprocessor interface part 105 which is provided between the line interface part 103 and the data communication part 104. For example, the interface part 105 includes a dual port random access memory (RAM).
The line interface part 103 is controlled by the CPU 101, but the data communication part 104 is controlled by the other CPU 102. A communication between the CPUs 101 and 102 is carried out via the interface part 105.
However, according to the communication control unit shown in FIG. 1, there is a problem in that the two CPUs 101 and 102 are required even for a data communication which uses a simple procedure. In addition, there is a problem in that the communication control unit cannot be used when realizing a plurality of data communications.